ADA4950-1YCPZ-R2 Analog Devices Inc, ADA4950-1YCPZ-R2 Datasheet - Page 24

Fixed Gain 1,2&3 Diff ADC Driver

ADA4950-1YCPZ-R2

Manufacturer Part Number
ADA4950-1YCPZ-R2
Description
Fixed Gain 1,2&3 Diff ADC Driver
Manufacturer
Analog Devices Inc
Type
Differential Amplifierr
Datasheet

Specifications of ADA4950-1YCPZ-R2

Amplifier Type
Differential
Number Of Circuits
1
Output Type
Differential
Slew Rate
2900 V/µs
-3db Bandwidth
750MHz
Voltage - Input Offset
200µV
Current - Supply
9.5mA
Current - Output / Channel
114mA
Voltage - Supply, Single/dual (±)
3 V ~ 11 V, ±1.5 V ~ 5.5 V
Operating Temperature
-40°C ~ 105°C
Mounting Type
Surface Mount
Package / Case
16-LFCSP
No. Of Amplifiers
1
Input Offset Voltage
2.5mV
Bandwidth
750MHz
Supply Voltage Range
3V To 11V
Supply Current
9.5mA
Amplifier Case Style
LFCSP
No. Of Pins
16
Rohs Compliant
Yes
Number Of Channels
1
Number Of Elements
1
Power Supply Requirement
Single/Dual
Common Mode Rejection Ratio
49dB
Voltage Gain Db
66dB
Single Supply Voltage (typ)
5/9V
Dual Supply Voltage (typ)
±3/±5V
Power Supply Rejection Ratio
84dB
Rail/rail I/o Type
No
Single Supply Voltage (min)
3V
Single Supply Voltage (max)
11V
Dual Supply Voltage (min)
±1.5V
Dual Supply Voltage (max)
±5.5V
Operating Temp Range
-40C to 105C
Operating Temperature Classification
Industrial
Mounting
Surface Mount
Pin Count
16
Package Type
LFCSP EP
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Gain Bandwidth Product
-
Current - Input Bias
-
Lead Free Status / Rohs Status
Compliant
ADA4950-1/ADA4950-2
HIGH PERFORMANCE ADC DRIVING
The ADA4950-x is ideally suited for broadband dc-coupled
applications. The circuit in Figure 63 shows a front-end
connection for an ADA4950-1 driving an
with dc coupling on the ADA4950-1 input and output. (The
AD9245 achieves its optimum performance when driven
differentially.) The ADA4950-1 eliminates the need for a
transformer to drive the ADC and performs a single-ended-to-
differential conversion and buffering of the driving signal.
The ADA4950-1 is configured with a single 3.3 V supply and a
gain of 2 for a single-ended input to differential output. The
57.6 Ω termination resistor, in parallel with the single-ended
input impedance of 375 Ω, provides a 50 Ω termination for the
source. The additional 26.7 Ω Thevenin resistance added to the
inverting input balances the parallel impedance of the 50 Ω
source and the termination resistor driving the noninverting
input. The required Thevenin bias voltage of 0.27 VDC applied
to the lower loop is obtained by scaling the VREF output of the
AD9245 and buffering it with the AD8031.
In this example, the 50 Ω signal generator has a 1 V p-p unipolar
open-circuit output voltage, and 0.5 V p-p output voltage when
terminated in 50 Ω. The V
tion and set externally with 1% resistors to maximize output
dynamic range on the tight 3.3 V supply.
1.0V
0.5V
0V
OCM
Figure 63. ADA4950-1 Driving an AD9245 ADC with Unipolar DC-Coupled Input and Output, Gain = 2
input is bypassed for noise reduc-
UNIPOLAR
SIGNAL
SOURCE
50Ω
1.0V p-p
0.1µF
10kΩ
10kΩ
AD9245
26.7Ω
0.1µF
57.6Ω
ADC,
NC
NC
10µF
500Ω
500Ω
250Ω
250Ω
+
V
Rev. 0 | Page 24 of 28
OCM
500Ω
ADA4950-1
500Ω
+3.3V
Because the inputs are dc-coupled, dc common-mode current
flows in the feedback loops, and a nominal dc level of 0.76 V is
present at the amplifier input terminals. A fraction of the output
signal is also present at the input terminals as a common-mode
signal; its level is equal to the ac output swing at the noninverting
output, divided down by the feedback factor of the lower loop. In
this example, this ripple is 0.5 V p-p × [276.7/(276.7 + 500)] =
0.18 V p-p. This ac signal is riding on the 0.76 V dc level, producing
a voltage swing between 0.67 V and 0.85 V at the input terminals.
This is well within the specified limits of 0.2 V to 1.5 V.
With an output common-mode voltage of 1.65 V, each ADA4950-1
output swings between 1.4 V and 1.9 V, opposite in phase, provid-
ing a gain of 2 and a 1 V p-p differential signal to the ADC input.
The differential RC section between the ADA4950-1 output and
the ADC provides single-pole low-pass filtering and extra buffering
for the current spikes that are output from the ADC input when
its SHA capacitors are discharged.
The AD9245 is configured for a 1 V p-p full-scale input by
connecting its SENSE pin to VREF, as shown in Figure 63.
0.1µF
0.1µF
AD8031
0.1µF
20pF
33Ω
33Ω
0.1µF
10µF
VIN+
+
VIN–
VREF SENSE
V
V
OUT, dm
OUT, cm
1.0kΩ
866Ω
AD9245
= +1.65V
= 1V p-p
AGND
AVDD
0.1µF

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